linux-kernel - Re: Regression with suspicious RCU usage splats with cpu

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Message-ID: <20170717060806.GC10026@atomide.com>
Date:   Sun, 16 Jul 2017 23:08:07 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Alex Shi <alex.shi@...aro.org>
Cc:     paulmck@...ux.vnet.ibm.com,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <Will.Deacon@....com>
Subject: Re: Regression with suspicious RCU usage splats with cpu_pm change

* Alex Shi <alex.shi@...aro.org> [170716 16:25]:
> I reused the rcu_irq_enter_irqson() from RCU_NONIDLE to avoid this issue. 
> It works fine.
> 
> Tony, Could you like to give a tested-by if this patch works for you.

Yeah that keeps things booting for me with no splats so:

Tested-by: Tony Lindgren <tony@...mide.com>

In general, it seems we're missing the knowledge in Linux kernel
of when the entire system is idle. Right now it seems that only
cpuidle_coupled knows that?

We could probably simplify things by adding some PM state for
entire system idle. Then cpuidle code and timer code could use
that to test when it's safe to do whatever the SoC needs to do
to enter deeper power states.

If we already have something like that, please do let me know :)

Regards,

Tony